Children with disseminated neuroblastoma have a very high risk of treatment failure and death despite receiving greatly intensified chemotherapy, underscoring the need to design novel molecular therapies for this disease, which constitutes the long-term goal of our proposal. However, recent efforts to discover promising molecular targets in this aggressive pediatric malignancy have revealed a very low somatic mutation rate, and the majority of high-risk tumors do not harbor druggable oncogenic proteins activated by somatic mutations, demonstrating that personalized therapeutic strategies will require insights well beyond those afforded by resequencing tumor DNA alone. This multiple principal investigator project will build on our recent genome- wide association study (GWAS) discovery of a robust genetic association at the LMO1 gene locus, which encodes a LIM-domain-only (LMO) transcriptional cofactor. Together, our published and unpublished preliminary data support a major oncogenic role for LMO1 in the most aggressive subset of neuroblastomas, and suggest the following central hypothesis: LMO1 is required for the initiation and maintenance of the malignant phenotype in a substantial subset of high-risk neuroblastoma cases. We propose to test this original concept in two integrated Specific Aims using the multi-PI leadership mechanism to bring together complementary research skills and resources available in the Maris and Look laboratories. In Aim 1, we will focus on how polymorphisms at the LMO1 locus alter regulatory mechanisms of the LMO1 gene in developing sympathetic nervous system cells to promote the initiation of neuroblastoma using genetic and epigenetic approaches in human-derived tissues and genome editing in the zebrafish model system. In Aim 2, we will focus on the mechanism by which LMO1 overexpression is somatically deregulated during malignant neuroblastic clonal evolution, and will seek to discover the key cellular networks that maintain the highly proliferative and metastatic phenotype characteristic of neuroblastomas high levels of LMO1 expression. The innovation of this project resides in the combined use of robust human (epi)genetic approaches with a novel and highly manipulable zebrafish model of neuroblastoma to address a fundamental problem with high clinical relevance. Our results will establish the requirement for LMO1 in neuroblastoma initiation, growth and survival. The work proposed here will serve as a roadmap for the investigation of GWAS discoveries in cancer and other human diseases, providing a paradigm for determining their mechanistic and clinical relevance.